It is the long range goal of this project to study interactions between connective tissue macromolecules as a way to understand connective tissue formation and structure. The topics of study are: 1) The mechanism of collagen fibril formation in vitro; 2) the role of non--colagenous macromolecules in collagen fibril architecture, and 3) the role of vitamin D metabolites in collagen fibril crosslinking in vivo. Previously, this laboratory developed a reproducible in vitro fibril assembly system and showed that type I collagen from rat tail tendon assembled into fibrils via a multistep process. This system is being used to study lathyritic Type I, lathyritic Type II, and Type III collagen assembly in vitro both in the presence and absence of proteoglycans and lysyl oxidase. The role of vitamin D metabolites in collagen crosslinking is being evaluated in vivo using vitamin D-deficient rachitic rats.